humidity. something about humidity fails more clones then anything else. The trick is to cover the clones for the first week. Clones dont have roots so they dont need very much nutrients and they dont need much light at all. I know some people stick their plants in dark, others use 24 hour light. It doesn't seem to make much difference, humidity is the key. Lots and lots of humidity for the first week, then after that, your clones should be able to survive anything.